The design and fabrication of solid nanomaterials are the key issues in heterogeneous catalysis to achieve desired performance.Traditionally,the main theme is to reduce the size of the catalyst particles as small as possible for maximizing the number of active sites.In recent years,the rapid advancement in materials science has enabled us to fabricate catalyst particles with tunable morphology.Consequently,both size modulation and morphology control of the catalyst particles can be achieved independently or synergistically to optimize their catalytic properties.In particular,morphology control of solid catalyst particles at the nanometer level can selectively expose the reactive crystal facets,and thus drastically promote their catalytic performance.In this review,we summarize our recent work on the morphology impact of Co3O4,CeO2 and Fe2O3 nanomaterials in catalytic reactions,together with related literature on morphology-dependent nanocatalysis of metal oxides,to demonstrate the importance of tuning the shape of oxide-nanocatalysts for prompting their activity,selectivity and stability,which is a rapidly growing topic in heterogeneous catalysis.The fundamental understanding of the active sites in morphology-tunable oxides that are enclosed by reactive crystal facets is expected to direct the development of highly efficient nanocatalysts.
Oxide nanostructures grown on noble metal surfaces are often highly active in many reactions,in which the oxide/metal interfaces play an important role.In the present work,we studied the surface structures of Fe Ox-on-Pt and Ni Ox-on-Pt catalysts and their activity to CO oxidation reactions using both model catalysts and supported nanocatalysts.Although the active Fe O1x structure is stabilized on the Pt surface in a reductive reaction atmosphere,it is prone to change to an Fe O2x structure in oxidative reaction gases and becomes deactivated.In contrast,a Ni O1x surface structure supported on Pt is stable in both reductive and oxidative CO oxidation atmospheres.Consequently,CO oxidation over the Ni O1x-on-Pt catalyst is further enhanced in the CO oxidation atmosphere with an excess of O2.The present results demonstrate that the stability of the active oxide surface phases depends on the stabilization effect of the substrate surface and is also related to whether the oxide exhibits a variable oxidation state.
Rentao MuQiang FuXiaoguang GuoXuejun XuDali TanXinhe Bao
Hexagonal β-Co(OH)2 nanosheets with edge length of 50 nm and thickness of 10 nm were hydrothermally synthesized with the aid of triethylamine.Upon calcination at 350°C in air,the β-Co(OH)2 nanosheets was converted into Co3O4 nanosheets with a similar dimension.Structural analyses during the calcination process identified that the β-Co(OH)2 precursor was initially dehydrated to HCoO2 and subsequently transferred into Co3O4.When being applied to catalyze CO oxidation at room temperature,the Co3O4 nanosheets exhibited a higher activity than the conventional spherical nanoparticles.This was perhaps related to the partial exposure of the{112}planes over the Co3O4 nanosheets.The porous structure generated during the calcination process also provided significant amounts of surface defects,which might contribute to the enhanced catalytic activity as well.
